This proposal outlines a series of experiments designed to test the regulation of an important intracellular pathway for controlling growth, cell death and patterning in developing organisms: that mediated by the Hippo and Warts protein kinases. This pathway plays a major role in controlling organ growth, and misregulation of the pathway is tumorigenic, but little is known about how it is controlled. We are concentrating on how this pathway is regulated by the large Drosophila protocadherins Fat and Dachsous. The extracellular domains of these two transmembrane proteins bind each other, and this suppresses growth by activating the Hippo pathway. However, the mechanisms connecting Fat and Dachsous to the Hippo pathway are poorly understood. First, we are dissecting the activities of the intracellular domains of Fat, and are using that to develop an in vitro RNAi screen for molecules required for Fat activity. Second, we are examining how boundaries and gradients of Fat and Dachsous expression, and the resultant polarization of Fat and Dachsous on cell surfaces, inhibits the Hippo pathway and triggers growth. Third, we are examining the role of a downstream negative regulator of Fat activity, the atypical myosin Dachs/Myosin29D, and its regulator Approximated. Finally, we are examining how the Hippo pathway combines with additional (especially spatial) information to regulate the expression of an important downstream target, the miRNA bantam. PUBLIC HEALTH RELEVANCE: The experiments test and refine our knowledge about how developing organisms precisely control their growth and patterning. Such precision is essential to normal human development, and failure in such precision underlies many pathologies, including genetic defects and cancers. The pathway being studied is an important means for controlling growth that is shared by humans and other organisms;it can be profitably examined in Drosophila because of Drosophila's genetic and molecular advantages, and the rigor and speed with which such studies can be performed.